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Amino acidic control of calcium phosphate precipitation by using the vapor diffusion method in microdroplets

机译：气相扩散法控制微滴中磷酸钙沉淀的氨基酸控制

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摘要

Calcium phosphate precipitation was carried out in the presence of L-aspartic acid (L-asp, iep = 2.77), L-alanine (L-ala, iep = 6.00), and L-arginine (L-arg, iep = 10.76) at different concentrations by using a vapor diffusion sitting drop method (VDSD) in microdroplets. Irrespective of the nature and the concentration of the amino acid used, the early stage in the precipitation consisted in the formation of a white viscous suspension composed of amorphous calcium phosphate (ACP) spherulites. After 1 week, different calcium phosphate phases were found depending on the amino acid nature and concentration. At higher concentrations of L-aspartic acid, brushite (dicalcium phosphate dihydrate, DCDP) platelets and a few needle-like carbonate- hydroxyapatite (HA) crystals were found. In the presence of higher concentrations of L-alanine, the precipitate was composed of both needle-like HA and octacalcium phosphate (OCP) platelets. Finally, at higher concentrations of L-arginine, we obtained carbonate-HA nanocrystals with length of 20 - 40 nm and a few OCP crystals, as in the blank experiment (without amino acids). The results are explained on the basis of the influence of these amino acids on the pH evolution of the solution and on the nature and strength of the interactions of the major charged species of the amino acids with the surface lattice ions of the apatite precursor phases (DCPD or OCP). A thermodynamic model, based on the temporal existence of OCP in the solution, is proposed to explain the formation of the HA nanocrystals.
机译：在L-天冬氨酸（L-asp，iep = 2.77），L-丙氨酸（L-ala，iep = 6.00）和L-精氨酸（L-arg，iep = 10.76）的存在下进行磷酸钙沉淀通过在微滴中使用蒸气扩散坐滴法（VDSD）在不同的浓度下不论所用氨基酸的性质和浓度如何，沉淀的早期阶段都是形成白色的粘性悬浮液，该悬浮液由无定形磷酸钙（ACP）球晶组成。 1周后，根据氨基酸的性质和浓度，发现了不同的磷酸钙相。在较高浓度的L-天冬氨酸中，发现透钙磷石（磷酸二钙二水合物，DCDP）血小板和一些针状碳酸盐-羟基磷灰石（HA）晶体。在较高浓度的L-丙氨酸存在下，沉淀物由针状HA和磷酸八钙（OCP）血小板组成。最终，与空白实验中一样（没有氨基酸），在更高浓度的L-精氨酸下，我们获得了长度为20-40 nm的碳酸盐-HA纳米晶体和一些OCP晶体。根据这些氨基酸对溶液pH演化的影响以及氨基酸的主要带电物质与磷灰石前体相的表面晶格离子的相互作用的性质和强度的说明来解释结果（ DCPD或OCP）。提出了基于溶液中OCP暂时存在的热力学模型来解释HA纳米晶体的形成。

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